Process for the conversion of stabilized acrylic fibers to carbon fibers

ABSTRACT

An improved process is provided for the thermal transformation of stabilized acrylic fibers to carbon fibers in an inert gaseous atmosphere wherein the highly toxic hydrogen cyanide gas which is simultaneously evolved from the fibrous material is effectively controlled and converted to a less toxic compound. A gaseous mixture of the inert gas and hydrogen cyanide is withdrawn from the heating zone wherein the thermal transformation is conducted and is contacted with an aqueous solution of cupric sulfate wherein the hydrogen cyanide gas undergoes chemical reaction to form an insoluble precipitate. The resulting precipitate may be optionally recovered from the aqueous solution.

United States Patent 1191 Ram et a1.

1 1 Oct. 21, 1975 154] PROCESS FOR THE CONVERSION OF STABILIZED ACRYLIC FIBERS TO CARBON FIBERS [73] Assignee: Celanese Corporation, New York,

221 Filed: Sept. 26, 1973 211 Appl. No.: 400,829

Related U.S. Application Data {63] Continuation of Ser. No. 228,959. Feb. 24, 1972,

abandoned.

[52] U.S. Cl. 423/447; 423/236; 423/379 [51] Int. Cl COlb 31/07 [58] Field of Search 423/447, 236, 379; 264/29 [56] References Cited UNITED STATES PATENTS 1,609,872 12/1926 Garner et al 423/236 2,088,003 7/1937 Sperr 423/236 X 2,140,605 12/1938 Sperr 423/236 3,539,295 11/1970 Ram 423/447 3,607,009 9/1971 Hess 423/379 7 FOREIGN PATENTS OR APPLICATIONS 802,284 10/1958 United Kingdom 423/236 OTHER PUBLICATIONS Watt et al., Applied Polymer Symposia," N0. 9, 215-227, (1969).

Primary Exuminer-Edward .I. Meros [5 7] ABSTRACT An improved process is provided for the thermal transformation of stabilized acrylic fibers to carbon fibers in an inert gaseous atmosphere wherein the highly toxic hydrogen cyanide gas which is simultaneously evolved from the fibrous material is effectively controlled and converted to a less toxic compound. A gaseous mixture of the inert gas and hydrogen cyanide is withdrawn from the heating zone wherein the thermal transformation is conducted and is contacted with an aqueous solution of cupric sulfate wherein the hydrogen cyanide gas undergoes chemical reaction to form an insoluble precipitate. The resulting precipitate may be optionally recovered from the aqueous solution.

16 Claims, 1 Drawing Figure US. Patent Oct. 21, 1975 MwZoP Q2 ,mmomum PROCESS FOR THE CONVERSION OF STABILIZED ACRYLIC FIBERS TO CARBON FIBERS This is a continuation, application Ser. No. 228,959, filed Feb. 24, 1972, now abandoned.

BACKGROUND OF THE DISCLOSURE In the search for high performance materials, considerable interest has been focused upon carbon fibers. The term carbon fibers is used herein in its generic sense and includes graphite fibers as well as amorphous carbon fibers. Graphite fibers are defined herein as fibers which consist substantially of carbon and have a predominant x-ray diffraction pattern characteristic of graphite. Amorphous carbon fibers, on the other hand, are defined as fibers in which the bulk of the fiber weight can be attributed to carbon and which exhibit a substantially amorphous x-ray diffraction pattern. Graphite fibers generally have a higher Youngs modulus than do amorphous carbon fibers and in addition are more highly electrically and thermally conductive.

Industrial high performance materials of the future are projected to make substantial utilization of fiber reinforced composites, and carbon fibers theoretically have among the best properties of any fiber for use as high strength reinforcement. Among these desirable properties are corrosion and high temperature resistance, low density, high tensile strength, and high modulus. Graphite is one of the very few known materials whose tensile strength increases with temperature. Uses for carbon fiber reinforced composites include aerospace structural components, rocket motor casings, deep-submergence vessels and ablative materials for heat shields on re-entry vehicles.

In the past procedures have been proposed and are generally known in the art for converting an acrylic fibrous precursor to an amorphous carbon form or to a graphitic carbon form which retains substantially the same fibrous configuration as the starting material. The acrylic fibrous material is first thermally stabilized, and then carbonized.

The thermal stabilization of an acrylic fibrous material in an oxygen-containing atmosphere is well known in the art and involves l an oxidative cross-linking reaction of adjoining molecules as well as (2) a cyclization reaction of pendant nitrile groups to a condensed dihydropyridine structure. The cyclization reaction is exothermic in nature and must be controlled if the fibrous configuration of the acrylic material is to be preserved. Accordingly, stabilization procedures commonly proposed are conducted for many hours (e.g., at 220C. for 3 to 7 hours, or more). During the carbonization reaction, elements in the stabilized fibrous material other than carbon, e.g., nitrogen, hydrogen, and oxygen, are expelled. The terms carbon fibers and carbonized fibrous material as used herein are defined to be materials consisting of at least about 90 percent carbon by weight, and preferably at least about 95 percent carbon by weight. Depending upon the conditions under which the carbonized fibrous product is processed, substantial amounts of graphitic carbon may or may not be present in the same as determined by the characteristic x-ray diffraction pattern of graphite.

It has been observed that when a previously stabilized acrylic fibrous material undergoes carbonization by heating in an inert gaseous atmosphere at a temperature in excess of about 300C., that substantial quantities of hydrogen cyanide gas are simultaneously evolved. Not only is such hydrogen cyanide gas extremely flammable, but it is an extremely hazardous poison which endangers operators in the area. I-Iydrogen cyanide can prove to be fatal to humans if swallowed, inhaled or absorbed through the skin. The potential hazard created by the hydrogen cyanide byproduct is particularly acute in those instances where stabilized acrylic fiber carbonization is attempted on a large scale such as by continuous passage of the fibrous precursor through an appropriate heating zone.

It is an object of the invention to provide an improved process for the thermal conversion of stabilized acrylic fibers to carbon fibers.

It is an object of the invention to provide a process for the thermal conversion of stabilized acrylic fibers to carbon fibers wherein the usual hazard created by the simultaneous evolution of hydrogen cyanide from the fibrous material is substantially eliminated.

It is another object of the invention to provide a process for the thermal conversion of stabilized acrylic fibers to carbon fibers wherein the evolved hydrogen cy anide by-product is controlled and converted to a less toxic form.

These and other objects, as well as the scope, nature and utilization of the process, will be apparent from the drawing and the following detailed description.

SUMMARY OF THE INVENTION It has been found that in a process for the production of a carbonaceous fibrous material wherein a stabilized acrylic fibrous material derived from an acrylonitrile homopolymer or an acrylonitrile copolymer containing at least about mol percent of acrylonitrile units and up to about 15 mol percent of one or more monovinyl units copolymerized therewith is positioned in a heat ing zone containing an inert gaseous atmosphere at a temperature in excess of 300C. to form a carbonaceous fibrous material containing at least about percent carbon by weight with the simultaneous evolution of hydrogen cyanide gas from the fibrous material, that improved results are achieved by:

a. withdrawing a gaseous mixture of the inert gas and hydrogen cyanide gas evolved during the heating from the heating zone, and

b. contacting the gaseous mixture following withdrawal from the heating zone with an aqueous solution of cupric sulfate wherein the hydrogen cyanide undergoes reaction with the cupric sulfate to form an insoluble precipitate.

DESCRIPTION OF THE DRAWING The drawing is a schematic presentation of a representative apparatus arrangement suitable for use in carrying out the claimed process on a continuous basis.

DESCRIPTION OF PREFERRED EMBODIMENTS It is essential that the acrylic fibrous material which is carbonized in accordance with the present process be preliminarily stabilized to a heat-resistant form. The term stabilized acrylic fibrous material as used herein is defined as an acrylic fibrous material which is non-burning when subjected to an ordinary match flame and capable of undergoing carbonization while retaining its original fibrous configuration essential intact. The stabilization reaction may be conducted by heating the acrylic material at relatively moderate temperatures. Such a stabilization procedure is commonly conducted in the presence of oxygen and results in the formation of a cyclized and preoxidized product which exhibits thermal stability not exhibited by the unmodi fied acrylic material. Stabilization procedures in which the cyclization reaction is catalyzed optionally may be employed. U.S. Ser. No. 749,957, filed Aug. 5, 1968 of Dagobert E. Stuetz (now abandoned); U.S. Pat. No. 3,539,295 to Michael J. Ram; and U.S. Pat. No. 3,592,595 to Klaus H. Gump and Dagobert E. Stuetz disclose representative preferred stabilization procedures. Each of the above-identified disclosures is assigned to the same assignee as the present invention and is herein incorporated by reference. Any other stabilization procedure capable of imparting thermal stability to the acrylic fibrous material may be selected.

The stabilized acrylic fibrous material is derived from a material formed primarily of recurring acrylonitrile units. For instance, the acrylic fibrous material should generally contain at least about 85 mol percent of acrylonitrile units and up to about mol percent of one or more monovinyl units copolymerized therewith, such as styrene, methyl acrylate, methyl methacrylate, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl pyridine, and the like. In a particularly preferred embodiment of the invention the stabilized acrylic fibrous material is derived from an acrylonitrile homopolymer. Preferred acrylonitrile copolymers contain no more than about 5 mol percent of one or more monovinyl comonomers copolymerized with acrylonitrile.

The stabilized acrylic fibrous material following stabilization in an oxygen-containing atmosphere commonly exhibits a carbon content of up to about 65 percent by weight, e.g., 50 to 65 percent by weight, a nitrogen content of at least about percent by weight (e.g., 20 to 30 percent by weight), and bound oxygen content of at least about 7 percent by weight (e.g., 7 to 12 percent by weight). The bound oxygen content may be determined by the Unterzaucher or other similar analysis.

The stabilized acrylic fibrous material which serves as the starting material in the present process may be provided in any one of a variety of physical configurations. The fibrous starting material is preferably provided as a continuous length. For instance, continuous multifilament yarns, strands, cables, and tows may be selected. In a particularly preferred embodiment of the process the stabilized acrylic fibrous material is a continuous multifilament yarn or a tow. The yarn may optionally be provided with a twist which improves its handling characteristics. For example, a twist of about 0.1 to 3 tpi, and preferably about 0.1 to 1.0 tpi, may be utilized.

In accordance with the present process the stabilized acrylic fibrous material is heated in an inert gaseous atmosphere at a temperature in excess of 300C. to form a carbonaceous fibrous material which contains at least about 90 percent carbon by weight, and most preferably at least about 95 percent carbon by weight. The carbonization heat treatment may be conducted on either a batch or continuous basis in accordance with techniques known in the art. Suitable inert gaseous atmospheres include nitrogen, argon, and helium.

In a preferred embodiment of the process, a continuous length of the stabilized acrylic fibrous material is continuously passed through a heating zone containing an inert gaseous atmosphere provided with a temperature gradient wherein the continuous length of fibrous material is elevated from a temperature of about 300C. to a temperature of about l00OC. to form a continuous length of carbonaceous fibrous material containing at least about percent carbon by weight, and most preferably at least about percent carbon by weight. If desired, the temperature gradient may be subsequently more highly elevated to about 2000 to 3100C. whereby substantial amounts of graphitic carbon are produced within the carbonaceous fibrous material. The presence of graphitic carbon in the fibrous product may be detected by the characteristic x-ray diffraction pattern of graphitic carbon.

The equipment utilized to produce the heating zone in which the carbonization reaction is conducted may be varied widely as will be apparent to those skilled in the art. For instance, induction furnaces wherein a graphite susceptor is encompassed by the windings of an induction coil, may be selected. Resistance heated furnaces may also be conveniently utilized.

Representative heating procedures for producing the carbonization and graphitization of a stabilized acrylic fibrous material are disclosed in commonly assigned U.S. Ser. No. 777,275, filed Nov. 20, 1968, of Charles M. Clarke (now abandoned) which is herein incorporated by reference. See also U.S. Pat. Nos. 3,508,874 to Richard N. Rulison and 3,539,295 to Michael J.

Ram.

It has been found that when a stabilized acrylic f1- brous material undergoes carbonization in an inert gaseous atmosphere having a temperature in excess of 300C. that substantial amounts of highly poisonous hydrogen cyanide gas are simultaneously evolved. More specifically, the evolution of hydrogen cyanide gas is substantial when the fibrous material is heated in an inert gaseous atmosphere at a temperature of about 300C. to 1000C. The evolution of hydrogen cyanide gas is particularly great when a continuous length of the stabilized acrylic fibrous material is passed through an inert gas carbonization heating zone provided with a temperature gradient wherein the fibrous material is elevated from a temperature of about 300C. to a temperature of about 1000C. In some carbonization/graphitization heat treatments, the quantity of hydrogen cyanide evolved during heating at about 300C. to 1000C. may approximate the weight of the graphitic carbon product.

In the improved carbonization process of the present invention, a gaseous mixture of the inert gas and the hydrogen cyanide gas evolved during the carbonization heating is withdrawn from the heating zone and contacted with an aqueous solution of cupric sulfate to form an insoluble precipitate. The hydrogen cyanide gas reacts with the cupric sulfate [CuSO to form a solid precipitate of cuprous cyanide [CuCN] and cupric cyanide [Cu(CN) In a preferred embodiment of the process (1 the inert gas is continuously introduced into the heating zone, (2) at least one stream of a gaseous mixture of the inert gas and hydrogen cyanide gas evolved during the heating is continuously withdrawn from the heating zone, and (3) the stream of the gaseous mixture following withdrawal from the heating zone is contacted with the aqueous solution of cupric sulfate wherein the hydrogen cyanide undergoes reaction with the cupric sulfate to form the insoluble precipitate.

The concentration of the cupric sulfate in the aqueous solution when contacted with the gaseous mixture may be varied widely, and is sufficient to at least substantially stoichiometrically react with the hydrogen cyanide present in the gaseous mixture. For instance, the aqueous solution of the cupric sulfate is preferably saturated, and provided ata temperature of about to 100C. (most preferably 50 to 95C.). If desired this cupric sulfate may be generated in situ through the reaction of sulfuric acid with metallic copper. The quantity of the gaseous mixture contacted with the aqueous solution of cupric sulfate is adjusted so that the hydrogen cyanide present therein is substantially completely reacted to form the solid precipitate, i.e., the quantity of hydrogen cyanide in the gaseous mixture should not stoichiometrically exceed the quantity of unreacted cu pric sulfate in the solution. In a preferred embodiment of the process, the contact between the gaseous mixture and the aqueous solution of cupric sulfate is accomplished by countercurrent flow through a tower provided with baffles, e.g., a packed or scrubbing tower. For instance, the gaseous mixture may be introduced at the bottom of a tower while the aqueous solution of cupric sulfate is passed down the tower.

The solid precipitate of cuprous cyanide and cupric cyanide produced in the present process is considerably less poisonous than the gaseous hydrogen cyanide evolved during the carbonization reaction and thereby substantially eliminates the acute hazard posed by the production of the gaseous hydrogen cyanide byproduct. If desired, the solid precipitate may be conveniently recovered from the aqueous solution, such as by decantation or centrifugation. The solid precipitate may be transported with considerably less danger than hydrogen cyanide. The cuprous cyanide precipitate may be used in double cyanide plating baths and as a catalyst in various organic reactions as known in the art. Upon contact of the precipitate with sulfuric acid, the hydrogen cyanide may be again regenerated immediately prior to its utilization in the production of acrylonitrile.

The carbon fibers produced in the process may be utilized as a high strength, lightweight, fibrous reinforcement when incorporated in a suitable matrix ma terial, e.g., a thermosetting resin or a metallic matrix.

The following example is given as a specific illustration of the invention. It should be understood, however, that the invention is hot limited to the specific details set forth in the example.

EXAMPLE In the description which follows, reference is made to the apparatus arrangement illustrated in the drawing.

The starting material selected for use in the process is a continuous length of a stabilized acrylonitrile homopolymer continuous filament yarn having a carbon content of about 62.6 percent by weight, a nitrogen content of about 24.5 percent by weight, a hydrogen content of about 2 percent and a bound oxygen content of about 1 1 percent by weight as determined by the Unterzaucher analysis. The stabilized acrylonitrile homopolymer yarn is non-burning when subjected to an ordinary match flame.

The starting material is derived from an 800 f1] dry spun acrylonitrile homopolymer continuous filament yarn having a total denier of about 1 150. The acrylonitrile homopolymer yarn is oriented by hot drawing following its formation to a single filament tenacity of about 3.5 grams per denier, and twisted to improve its handling characteristics at a twist of about 0.5 tpi. The yarn is stabilized by continuous passage for 120 minutes through a muffle furnace containing an air atmosphere maintained at 270C. in accordance with the teachings of US. Ser. No. 749,957 filed Aug. 5, 1968 of Dagobert E. Stuetz (now abandoned). During the stabilization reaction no substantial amount of hydrogen cyanide gas is evolved from the fibrous material (i.e., about 2.3 percent by weight hydrogen cyanide gas).

The stabilized acrylonitrile homopolymer yarn is provided upon rotating feed bobbin 1, and is continuously unwound from the same prior to continuously passing through a Lepel 450 KC induction furnace 2 wherein it undergoes carbonization and graphitization prior to being taken up on rotating takeup bobbin 4. A graphite tube susceptor 6 having a length of 8 /2 inches, an outer diameter of V2 inch, and an inner diameter of /8 inch is positioned within induction furnace 2 and is encompassed by a copper coil 8 having a length of one inch which is attached to a high frequency power source (not shown). The copper coil 8 which encompasses a portion of the hollow graphite tube susceptor 6 is positioned at a location substantially equidistant from the respective ends of the graphite tube susceptor 6. An enclosure 10 provided with appropriate entrance and exit openings surrounds the graphite tube susceptor 6 and the copper coil 8.

The stabilized acrylonitrile homopolymer yarn is continuously passed from rotating feed bobbin 1 to rotating takeup bobbin 4 at a speed of 3 inches per minute. The yarn is at room temperature (i.e., 25C.) as it approaches the induction furnace 2 and while passing through the heating zone present therein is subjected to a circulating heated nitrogen atmosphere provided with a temperature gradient wherein it is heated to a maximum temperature of about 2800C. While passing through the temperature gradient of the heating zone, a substantial amount of hydrogen cyanide gas is evolved as the fibrous material undergoes carbonization and is heated from a temperature of about 300C. to a temperature of about 1000C. Substantial amounts of graphitic carbon are formed as the fibrous material is elevated to 2800C. The resulting graphitic carbon yarn contains in excess of 99 percent carbon by weight.

Throughout the passage of the fibrous material through the heating zone, a stream of nitrogen gas is continuously introduced into enclosure 10 via line 12. Also, a stream ofa gaseous mixture of nitrogen and hydrogen cyanide is continuously withdrawn from induction furnace 2 via line 14 which passes through enclosure 10 and communicates with an opening in the wall of graphite tube susceptor 6. The gaseous mixture is discharged from line 14 into the bottom of scrubbing tower 16 which is packed with ceramic rings (not shown) along the length of its interior which are supported upon a series of slotted plates.

Within vessel 18 is provided a saturated aqueous solution 20 containing cupric sulfate which is provided at about C. A portion of cupric sulfate solution 20 is continuously withdrawn through line 22 and is introduced into the top of the packed tower 16 where it contacts the upwardly flowing gaseous mixture introduced via line 14. Upon contact the hydrogen cyanide of the gaseous mixture undergoes chemical reaction to form a solid precipitate of cuprous cyanide and cupric cyanide. Nitrogen gas may be withdrawn from the tower 16 via line 17. The solid precipitate while suspended in the solution together with a sulfuric acid byproduct is withdrawn from the bottom of tower 16 via line 24 and returned to vessel 18. The solid precipitate 26 is allowed to settle to the bottom of vessel 18 and may be withdrawn through valve 28. Metallic copper rods 32 immersed in solution 20 make possible the regeneration of the cupric sulfate solution upon the reaction of the sulfuric acid by-product with the same.

Although the invention has been described with preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the claims appended hereto.

We claim:

1. In a process for the production of a carbonaceous fibrous material wherein a stabilized acrylic fibrous material derived from an acrylonitrile homopolymer or an acrylonitrile copolymer containing at least about 85 mol percent of acrylonitrile units and up to about 15 mol percent of one or more monovinyl units copolymerized therewith is positioned in a heating zone containing an inert gaseous atmosphere at a temperature in excess of 300C. to form a carbonaceous fibrous material containing at least about 90 percent carbon by weight with the simultaneous evolution of hydrogen cyanide gas from said fibrous material; the improvement comprising:

a. withdrawing a gaseous mixture of said inert gas and hydrogen cyanide gas evolved during said heating from said heating zone, and

b. contacting via countercurrent flow said gaseous mixture following withdrawal from said heating zone with an aqueous solution of cupric sulfate wherein said hydrogen cyanide undergoes reaction with said cupric sulfate to form an insoluble precipitate.

2. An improved process according to claim 1 wherein said stabilized acrylic fibrous material is derived from an acrylonitrile homopolymer.

3. An improved process according to claim 1 wherein said stabilized acrylic fibrous material is derived from an acrylonitrile copolymer which contains at least about 95 mol percent of acrylonitrile units and up to about mol percent of one or more monovinyl units copolymerized therewith.

4. An improved process according to claim 1 wherein said inert gas is selected from the group consisting of nitrogen, argon, and helium.

5. An improved process according to claim 1 which includes the additional step of (c) recovering said insoluble precipitate from said aqueous solution.

6. In a process for the continuous production of a carbonaceous fibrous material wherein a continuous length of a stabilized acrylic fibrous material derived from an acrylonitrile homopolymer or an acrylonitrile copolymer containing at least about 85 mol percent of acrylonitrile units and up to about mol percent of one or more monovinyl units copolymerized therewith is continuously passed through a heating zone containing an inert gaseous atmosphere provided with a temperature gradient wherein said continuous length of fibrous material is elevated from a temperature of about 300C. to a temperature of about 1000C. to form a continuous length of carbonaceous fibrous material containing at least about percent carbon by weight with the simultaneous evolution of hydrogen cyanide gas from said fibrous material; the improvement comprising:

a. continuously introducing said inert gas into said heating zone,

b. continuously withdrawing at least one stream of a gaseous mixture of said inert gas and hydrogen cyanide gas evolved during said heating from said heating zone, and

c. contacting via countercurrent flow said stream of said gaseous mixture following withdrawal from said heating zone with an aqueous solution of cupric sulfate wherein said hydrogen cyanide undergoes reaction with said cupric sulfate to form an insoluble precipitate.

7. An improved process according to claim 6 wherein said stabilized acrylic fibrous material is derived from an acrylonitrile homopolymer.

8. An improved process according to claim 6 wherein said stabilized acrylic fibrous material is derived from an acrylonitrile copolymer which contains at least about mol percent of acrylonitrile units and up to about 5 mol percent of one or more monovinyl units copolymerized therewith.

9. An improved process according to claim 6 wherein said continuous length of stabilized acrylic fibrous material comprises at least one continuous multifilament yarn.

10. An improved process according to claim 6 wherein said continuous length of stabilized acrylic fibrous material is a tow.

11. An improved process according to claim 6 wherein said inert gas is selected from the group consisting of nitrogen, argon, helium.

12. An improved process according to claim 6 wherein said aqueous solution of cupric sulfate when contacted with said gaseous mixture is substantially saturated with cupric sulfate and is provided at a temperature of about 20 to C.

13. An improved process according to claim 6 which includes the additional step of (d) recovering said insoluble precipitate from said aqueous solution.

14. In a process for the continuous production of carbonaceous fibrous material wherein a continuous length ofa stabilized acrylonitrile homopolymer having a carbon content of up to about 65 percent by weight, a nitrogen content of at least about 20 percent by weight, and a bound oxygen content of at least about 7 percent by weight is continuously passed through a heating zone containing an inert gaseous atmosphere selected from the group consisting of nitrogen, argon, and helium provided with a temperature gradient wherein said continuous length of fibrous material is elevated from a temperature of about 300C. to a temperature of about 1000C. to form a continuous length of carbonaceous fibrous material containing at least about 90 percent carbon by weight with the simultaneous evolution of hydrogen cyanide gas from said fi brous material; the improvement comprising:

a. continuously introducing said inert gas into said heating zone,

b. continuously withdrawing at least one stream of a gaseous mixture of said inert gas and hydrogen cyanide evolved during said heating from said heating zone,

15. An improved process according to claim 14 wherein said continuous length of stabilized acrylic fibrous material comprises at least one continuous multifilament yarn. I

16. An improved process according to claim 14 wherein said continuous length of stabilized acrylic fibrous material is a tow. 

1. IN A PROCESS FOR THE PRODUCTION OF A CARBONACEOUS FIBROUS MATERIAL WHEREIN A STABILIZED ACRYLIC FIBROUS MATERIAL DERIVED FROM AN ACRYLONITRILE HOMOPOLYMER OR AN ACRYLONITRILE COPOLYMER CONTAINING AT LEAST ABOUT 85 MOL OF ACRYLONITRILE UNITS AND UP TO ABOUT 15 MOL PERCENT OF ONE OR MORE MONOVINYL UNITS COPOLYMERIZED THEREWITH IS POSITIONED IN A HEATING ZONE CONTAINING AN INERT GASEOUS ATMOSPHERE AT A TEMPERATURE IN EXCESS OF 300*C. TO FORM A CARBONACEOUS FIBROUS MATERIAL CONTAINING AT LEAST ABOUT 90 PERCENT CARBON BY WEIGHT WITH THE SIMULANEOUS EVOLUTION OF HYDROGEN CYANIDE GAS FROM SAID FIBROUS MATERIAL, THE IMPROVEMENT COMPRISING: A. WITHDRAWING A GASEOUS MIXTURE OF SAID INERT GAS AND HYDROGEN CYANIDE GAS EVOLVED DURING SAID HEATING FROM SAID HEATING ZONE, AND B. CONTACTING VIA COUNTERCURRENT FLOW SAID GASEOUS MIXTURE FOLLOWING WITHDRAWAL FROM SAID HEATING ZONE WITH AN AQUEOUS SOLUTION OF CUPRIC SULFATE WHEREIN SAID HYDROGEN CYANIDE UNDERGOES REACTION WITH SAID CUPRIC SULFATE TO FORM AN INSOLUBLE PRECIPITATE.
 2. An improved process according to claim 1 wherein said stabilized acrylic fibrous material is derived from an acrylonitrile homopolymer.
 3. An improved process according to claim 1 wherein said stabilized acrylic fibrous material is derived from an acrylonitrile copolymer which contains at least about 95 mol percent of acrylonitrile units and up to about 5 mol percent of one or more monovinyl units copolymerized therewith.
 4. An improved process according to claim 1 wherein said inert gas is selected from the group consisting of nitrogen, argon, and helium.
 5. An improved process according to claim 1 which includes the additional step of (c) recovering said insoluble precipitate from said aqueous solution.
 6. In a process for the continuous production of a carbonaceous fibrous material wherein a continuous length of a stabilized acrylic fibrous material derived from an acrylonitrile homopolymer or an acrylonitrile copolymer containing at least about 85 mol percent of acrylonitrile units and up to about 15 mol percent of one or more monovinyl units copolymerized therewith is continuously passed through a heating zone containing an inert gaseous atmosphere provided with a temperature gradient wherein said continuous length of fibrous material is elevated from a temperature of about 300*C. to a temperature of about 1000*C. to form a continuous length of carbonaceous fibrous material containing at least about 90 percent carbon by weight with the simultaneous evolution of hydrogen cyanide gas from said fibrous material; the improvement comprising: a. continuously introducing said inert gas into said heating zone, b. continuously withdrawing at least one stream of a gaseous mixture of said inert gas and hydrogen cyanide gas evolved during said heating from said heating zone, and c. contacting via countercurrent flow said stream of said gaseous mixture following withdrawal from said heating zone with an aqueous solution of cupric sulfate wherein said hydrogen cyanide undergoes reaction with said cupric sulfate to form an insoluble precipitate.
 7. An improved process according to claim 6 wherein said stabilized acrylic fibrous material is derived from an acrylonitrile homopolymer.
 8. An improved process according to claim 6 wherein said stabilized acrylic fibrous material is derived from an acrylonitrile copolymer which contains at least about 95 mol percent of acrylonitrile units and up to about 5 mol percent of one or more monovinyl units copolymerized therewith.
 9. An improved process according to claim 6 wherein said continuous length of stabilized acrylic fibrous material comprises at least one continuous multifilament yarn.
 10. An improved process according to claim 6 wherein said continuous length of stabilized acrylic fibrous material is a tow.
 11. An improved process according to claim 6 wherein said inert gas is selected from the group consisting of nitrogen, argon, helium.
 12. An improved process according to claim 6 wherein said aqueous solution of cupric sulfate when contacted with said gaseous mixture is substantially saturated with cupric sulfate and is provided at a temperature of about 20* to 100*C.
 13. An improved process according to claim 6 which includes the additional step of (d) recovering said insoluble precipitate from said aqueous solution.
 14. In a process for the continuous production of carbonaceous fibrous material wherein a continuous length of a stabilIzed acrylonitrile homopolymer having a carbon content of up to about 65 percent by weight, a nitrogen content of at least about 20 percent by weight, and a bound oxygen content of at least about 7 percent by weight is continuously passed through a heating zone containing an inert gaseous atmosphere selected from the group consisting of nitrogen, argon, and helium provided with a temperature gradient wherein said continuous length of fibrous material is elevated from a temperature of about 300*C. to a temperature of about 1000*C. to form a continuous length of carbonaceous fibrous material containing at least about 90 percent carbon by weight with the simultaneous evolution of hydrogen cyanide gas from said fibrous material; the improvement comprising: a. continuously introducing said inert gas into said heating zone, b. continuously withdrawing at least one stream of a gaseous mixture of said inert gas and hydrogen cyanide evolved during said heating from said heating zone, c. contacting via countercurrent flow said stream of said gaseous mixture following withdrawal from said heating zone with a substantially saturated aqueous solution of cupric sulfate provided at a temperture of about 50* to 95*C. wherein said hydrogen cyanide undergoes reaction with said cupric sulfate to form an insoluble precipitate, and d. recovering said insoluble precipitate from said aqueous solution.
 15. An improved process according to claim 14 wherein said continuous length of stabilized acrylic fibrous material comprises at least one continuous multifilament yarn.
 16. An improved process according to claim 14 wherein said continuous length of stabilized acrylic fibrous material is a tow. 